Colored silicone rubber adhesive film and methods of use

ABSTRACT

A colored silicone rubber adhesive film and methods of adhesion by means of the silicone rubber adhesive film are disclosed. The silicone rubber adhesive film comprises (A) an organopolysiloxane; (B) a wet method hydrophobized reinforcing silica; (C) an organohydridopolysiloxane; (D) an azo or anthroquinone pigment, and (E) a curing accelerator. The colored silicone rubber adhesive film is easily handled, possesses excellent workability, and most important, makes it possible to verify the degree and the point of completion of the curing due to the presence of the pigment.

[0001] This application is a divisional of U.S. patent application Ser.No. 09/238,350, filed Jan. 27, 1999, pending.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a silicone rubber adhesive filmand to methods for adhering metal substrates to glass substrates.

[0003] Silicone rubber adhesive films are known. For example, JapaneseOfficial Patent Publication (Kokoku) Heisei 7-119394 discloses asilicone rubber adhesive film prepared from an organopolysiloxane rubberand a wet method hydrophobized reinforcing silica with a curingaccelerator. The silicone rubber adhesive film is simple to handle,possesses excellent workability, and is suitable for firmly securingtogether plates which have smooth surfaces and are made of suchmaterials as glass, metal, etc. Furthermore, since the silicone rubberadhesive film can fix together glass and metal plates, it can beadvantageously used as an adhesive for attaching knobs to glass entrancedoors or to glass windows for buildings, for attaching mirrors (socalled inner mirrors) to automobile windshield, etc. However, theadhesive strength of the silicone rubber adhesive film depends on thedegree of its curing, and therefore there may be significant variationsin the strength of the connections between structural elements securedwith the use of this adhesive.

[0004] It is an object of the present invention to provide a coloredsilicone rubber adhesive film which is easily handled, possessesexcellent workability, and most important, makes it possible to verifythe degree and the point of completion of the curing in the siliconerubber adhesive film. When the latter is used for bonding varioussubstrates together, it produces adhesive connections with improveduniformity.

[0005] Another object of the present invention is to provide methods foradhering metals substrates to glass substrates with the use of thecolored silicone rubber adhesive film.

[0006] As a results of careful studies aimed at the solution of theproblems described above, the present inventors have found certainorganic pigments when present in a specific transparent silicone rubberadhesive film creates a colored film. The colored silicone rubber filmbecomes colorless upon subsequent heating and curing. This feature isused to verify the degree of curing, so that the moment at which theadhesive becomes completely colorless, curing completion is indicated.Furthermore, the inventors have discovered that the colored siliconerubber adhesive film produces bonded structures with improved uniformityin adhesive strength.

SUMMARY OF THE INVENTION

[0007] The present invention provides a colored silicone-rubber adhesivefilm composition comprising:

[0008] (A) 100 parts by weight of an organopolysiloxane with an averageunit formula R_(a)SiO_((4-a)/2), where R is a substituted orunsubstituted hydrocarbon group with the provisio that at least two Rgroups are alkenyl groups, and a is a number between 1.9 and 2.1;

[0009] (B) 30 to 150 parts by weight of a wet method hydrophobizedreinforcing silica having a specific surface area exceeding 200 m²/g,consisting essentially of SiO_(4/2) units and organopolysiloxane unitsselected from the group consisting of R₃SiO_(1/2) units, R₂SiO_(2/2)units, RSiO_(3/2) units, and mixtures thereof, where R is the same asdefined above,

[0010] wherein the mole ratio of the organopolysiloxane units to theSiO_(4/2) units is within a range of 0.08 to 2.0;

[0011] (C) 0.1 to 10 parts by weight of an organohydridopolysiloxanecomprising at least one silicon-bonded hydrogen atom;

[0012] (D) a pigment selected from the group of azo pigments andanthroquinone pigments present in an amount sufficient for coloring asilicone rubber adhesive film composition;

[0013] (E) a curing accelerator in an amount sufficient to cure thesilicone rubber adhesive film composition;

[0014] wherein said colored silicone rubber adhesive film compositionhas a tensile strength of 1.5 kg/cm² to 5.0 kg/cm² at 25° C.

[0015] The inventors also provide a method of adhering a metal substrateto a glass substrate comprising:

[0016] a) coating the surface of a metal substrate with a primercomposition comprising a organosilicon compound selected from the groupof silanes and organosiloxane oligimers having an alkoxy group to form aprimer layer;

[0017] b) laminating said primer layer with the colored silicone rubberadhesive film;

[0018] c) bringing the surface of said colored silicone rubber adhesivefilm into contact with a glass substrate;

[0019] d) curing said colored silicone rubber adhesive film compositionat a temperature above 80° C. until the said colored silicone rubberadhesive film composition becomes colorless.

[0020] In another embodiment of adhering a metal substrate to a glasssubstrate, a method is provided comprising:

[0021] a) coating the surface of a metal substrate with a primercomposition comprising,

[0022] i) an organosilicon compound having an alkoxy group selected fromthe group of silanes and organosiloxane oligimers, and

[0023] ii) a pigment selected from the group of azo pigments andanthroquinone pigments

[0024] to form a colored primer layer on the surface of said metalsubstrate;

[0025] b) laminating said colored primer layer with a silicone rubberadhesive film composition comprising,

[0026] (A) 100 parts by weight of an organopolysiloxane with an averageunit formula R_(a)SiO_((4-a)/2), where R is a substituted orunsubstituted hydrocarbon group with the provisio that at least two Rgroups are alkenyl groups, and a is a number between 1.9 and 2.1;

[0027] (B) 30 to 150 parts by weight of a wet method hydrophobizedreinforcing silica; having a specific surface area exceeding 200 m²/g,consisting essentially of SiO_(4/2) units and organopolysiloxane unitsselected from the group consisting of R₃SiO_(1/2) units, R₂SiO_(2/2)units, RSiO_(3/2) units, and mixtures thereof, where R is the same asdefined above,

[0028] wherein the mole ratio of the organopolysiloxane units to theSiO_(4/2) units is within a range of 0.08 to 2.0;

[0029] (C) 0.1 to 10 parts by weight of an organohydridopolysiloxanecomprising at least one silicon-bonded hydrogen atom;

[0030] (D) a curing accelerator in an amount sufficient to cure thesilicone rubber adhesive film composition;

[0031] wherein said silicone rubber adhesive film composition has atensile strength of 1.5 kg/cm² to 5.0 kg/cm² in an uncured state at 25°C.;

[0032] c) maintaining contact between the silicone rubber adhesive filmand the colored primer layer for at least one hour to form a coloredsilicone rubber adhesive layer;

[0033] d) bringing the surface of said colored silicone rubber adhesivefilm into contact with a glass substrate, and

[0034] e) curing said colored silicone rubber adhesive film by heatingat a temperature above 80° C. until the film becomes colorless.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035]FIG. 1 is schematic view of the structure obtained in step (1) ofExample 2 of the present invention (the structure consists of astainless steel substrate with a layer of red primer applied onto thesurface of the substrate).

[0036]FIG. 2 is a schematic view of a laminated structure consisting ofa transparent silicone rubber adhesive film layer applied onto thesurface of the primer layer obtained in the initial part of step (2) ofExample 2 of the invention.

[0037]FIG. 3 is a schematic view of the structure obtained in the finalstage of step 2 of Example 2 (this structure was obtained by forming ared primer layer on the surface of the stainless-steel substrate,placing a red silicone rubber adhesive film onto the surface of theprimer layer, and then bringing the surface of the colored siliconerubber adhesive film into contact with the surface of a glasssubstrate).

[0038]FIG. 4 is a schematic view of an integral structure in which ametal substrate obtained in Example 2 of the invention is adhesivelyconnected to a glass substrate via a transparent cured silicone rubberadhesive film.

DETAILED DESCRIPTION OF THE INVENTION

[0039] The present invention provides a colored silicone-rubber adhesivefilm composition comprising:

[0040] (A) 100 parts by weight of an organopolysiloxane with an averageunit formula R_(a)SiO_((4-a)/2), where R is a substituted orunsubstituted hydrocarbon group with the provisio that at least two Rgroups are alkenyl groups, and a is a number between 1.9 and 2.1;

[0041] (B) 30 to 150 parts by weight of a wet method hydrophobizedreinforcing silica having a specific surface area exceeding 200 m²/g,consisting essentially of SiO_(4/2) units and organopolysiloxane unitsselected from the group consisting of R₃SiO_(1/2) units, R₂SiO_(2/2)units, RSiO_(3/2) units, and mixtures thereof, where R is the same asdefined above,

[0042] wherein the mole ratio of the organopolysiloxane units to theSiO_(4/2) units is within a range of 0.08 to 2.0;

[0043] (C) 0.1 to 10 parts by weight of an organohydridopolysiloxanecomprising at least one silicon-bonded hydrogen atom;

[0044] (D) a pigment selected from the group of azo pigments andanthroquinone pigments present in an amount sufficient for coloring asilicone rubber adhesive film composition;

[0045] (E) a curing accelerator in an amount sufficient to cure thesilicone rubber adhesive film composition;

[0046] wherein said colored silicone rubber adhesive film compositionhas a tensile strength of 1.5 kg/cm² to 5.0 kg/cm² at 25° C.

[0047] The organopolysiloxane component (A), of the silicone rubbercomposition of the present invention has a structure with an averageunit formula R_(a)SiO_((4-a)/2), where R is a substituted orunsubstituted hydrocarbon group with the provisio that at least two Rgroups are alkenyl groups, and a is a number between 1.9 and 2.1. R inthis structure designates an alkyl group such as; a methyl group, ethylgroup, propyl group or a similar alkyl group; a vinyl group, allyl groupor a similar alkenyl group; a cyclohexyl group or a similar cycloalkylgroup; a (-phenylethyl group or a similar aralkyl group; a phenyl group,tolyl group, or a similar aryl group; a chloromethyl group,3-chloropropyl group, 3,3,3-trifluoropropyl group, or a similarsubstituted or unsubstituted monovalent hydrocarbon group exemplified bya halogenated alkyl group; a is on average between 1.9 and 2.1. It ispreferred that the organopolysiloxane contain at least two lower-alkenylgroups in one molecule. Structurally, this organopolysiloxane may bepurely linear, or branched to some degree.

[0048] The viscosity and degree of polymerization of theorganopolysiloxane may vary within the limits typical oforganopolysiloxanes known in the art. However, it is preferred theorganopolysiloxane used in this invention have a viscosity greater than1×10⁶ mm²/s at 25° C., and have an average degree of polymerizationgreater than 3000.

[0049] The organopolysiloxane is exemplified by the following compounds:a dimethylpolysiloxane having dimethylvinylsiloxy terminal group; acopolymer of a methylvinylsiloxane and dimethylsiloxane havingdimethylvinylsiloxy terminal group; a copolymer of amethylphenylsiloxane and a dimethylsiloxane having dimethylvinylsiloxyterminal group; a copolymer of a methylvinylsiloxane,methylphenylsiloxane, and a dimethylsiloxane having adimethylvinylsiloxy terminal group; a copolymer of methylvinylsiloxaneand a dimethylsiloxane having a trimethylsiloxy terminal group; acopolymer of a methylvinylsiloxane, methylphenylsiloxane, and adimethylsiloxane having trimethylsiloxy terminal group, etc.

[0050] The wet method hydrophobized reinforcing silica, whichconstitutes component (B) of the composition of the present invention,improves the tensile strength of the silicone rubber adhesive film in anuncured state. Furthermore, it improves the adhesion of the siliconerubber adhesive to various substrates after heating and curing, inparticular improving the durability of the adhesive connection. The wetmethod hydrophobized reinforcing silica has a specific surface areaabove 200 m²/g, it comprises organopolysiloxane units selected from agroup consisting essentially of R₃SiO_(1/2) units, R₂SiO_(2/2) units,RSiO_(3/2) units or their mixtures (where R is the same as definedabove) and SiO_(4/2) units. The organopolysiloxane units should be usedin an amount sufficient for hydrophobization of the reinforcing silica.It is preferred that a mole ratio of organopolysiloxane units toSiO_(4/2) units be within a range of 0.08 to 1.5. If this ratio is lessthan 0.08, the composition may lose its adhesive characteristics, and ifthe ratio exceeds 1.5, the reinforcing properties are impaired so thatthe composition cannot be used as a filler with reinforcing properties.This component can be produced by methods described in Official JapanesePatent Publication (Kokoku) 61-56255 or in U.S. Pat. No. 4,418,165,incorporated herein by reference.

[0051] The organohydridopolysiloxane containing a silicon-bondedhydrogen atom which constitutes component (C), is represented by thefollowing compounds: a methylhydridopolysiloxane having atrimethylsiloxy group at both molecular terminals; a copolymer of amethylhydridosiloxane and a dimethylsiloxane having trimethylsiloxygroups on both terminals; a copolymer of a methylhydridosiloxane and amethylphenylsiloxane having dimethylphenylsiloxy groups on bothterminals; and a copolymer consisting of a cyclicmethylhydridopolysiloxane, dimethylhydridosiloxane units, and SiO_(4/2)units.

[0052] The curing accelerator, which constitutes component (E), is acatalyst for curing the composition of the present invention. Thiscatalyst may be represented by an organic peroxide, a combination of anorganic peroxide with a platinum catalyst, or a platinum catalyst alone.The following are examples of organic peroxides: dicumyl peroxide,di-t-butyl peroxide, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy) hexane, 2,5-dimthyl-2,5-di (t-butylperoxy) hexyne,1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, benzoyl peroxide,0-methylbenzoyl peroxide, P-methylbenzoyl peroxide.

[0053] Platinum catalysts are exemplified by chloroplatinic acid, analcoholic denaturate of chloroplatinic acid, platinum chelate, acoordination compound of chloroplatinic acid and olefins, a complex ofchloroplatinic acid and tetramethyldivinylsiloxane. It is preferred thatthis component be used in an amount sufficient for curing thecomposition of the present invention. The organic peroxide is typicallyused in an amount of 0.1 to 10 parts by weight. The platinum catalyst,is typically used in an amount of 1 to 500 parts by weight, preferably 1to 300 parts by weight against 1×10⁶ parts by weight of component (A).

[0054] The colored silicone rubber adhesive film composition of thepresent invention comprises components (A) through (E). However, thecomposition may also contain an adhesion accelerator as a component (F)which may be added for improving adhesion to the substrate. Examples ofthis component are organoalkoxysilanes which contain mercapto groups,amino groups, vinyl groups, allyl groups, hexenyl groups, methacryloxygroups, acryloxy groups, glycidoxy groups, or similar organic functionalgroups, or the products of partial hydrolyzation and condensation of theorganoalkoxysilanes.

[0055] The said adhesion accelerators are represented byγ-mercaptopropyl-trimethoxysilane,γ-mercaptopropyl-methyldimethoxysilane, γ-(2-aminoethyl)-aminopropyltrimethoxysilane, γ-(2-aminoethyl)-aminopropylmethyl dimethoxysilane,γ-methacryloxypropyl trimethoxysilane, γ-acryloxypropyltrimethoxysilane, vinyltri (methoxyethoxy)silane, allyltrimethoxysilane, γ-glycidoxypropyl trimethoxysilane, or by the products of theirpartial hydrolyzation. If used, it is preferred that the adhesionaccelerator be used in an amount of 0.1 to 10 parts by weight per 100parts of component (A).

[0056] The silicone rubber adhesive film of the present invention isobtained by first kneading the components (A) through (E) inpredetermined proportions to form a silicone rubber composition.Kneading can be accomplished, for example, with a mixer such as atwo-roller type, a kneader, a Banbury's mixer, etc. It is preferred thatthe silicone rubber composition have a tensile strength within the rangeof 1.5 kg/cm² to 5.0 kg/cm², and preferably between 2.0 kg/cm² to 4.0kg/cm² in an uncured state at 25° C. A tensile strength below 1.5 kg/cmwill lead either to deformation in shape during handling, or to tearing.If, on the other hand, the tensile strength exceeds 5.0 kg/cm², thecomposition will be easy to handle, but will be subject to reverseplastization. Subsequently, reverse plastization causes the compositionto become hard, loose its plasticity, and develop cracks. The tensilestrength in the uncured silicone rubber composition of the presentinvention is measured in accordance with the procedure of JIS K 6301(JIS—Japanese Industrial Standard).

[0057] The silicone rubber adhesive film of the present invention can beproduced for example by extruding the silicone rubber compositionthrough an extruder having a nozzle of appropriate dimensions.Alternatively, the silicone rubber composition can be shaped into afilm-like form between calender rollers and then split into severalstrips.

[0058] It is important that the silicone rubber adhesive film of thepresent invention have a uniform thickness. It is preferred that thisthickness be within a range of 0.01 to 10 mm, preferably between 0.05 mmand 5 mm. If the silicone rubber adhesive film is thinner than 0.01 mm,it will be difficult to form into a film-like shape. If it is thickerthan 10 mm, the increased stress on the interface results in a decreasein adhesive strength or to an increase in creeping.

[0059] For practical use of the silicone rubber adhesive film of thepresent invention, it is advantageous to stamp out pieces that match inshape the substrate to be adhered.

[0060] The silicone rubber adhesive film of the present invention iscolored by the addition of a pigment. The pigment, component (D), isselected from azo pigments or anthraquinone pigments. The azo pigmentare exemplified by monoazo pigments, polyazo pigments, pyrazolonepigments, stilbene azo pigments, thiazole azo pigments. Disazo pigmentsare represented by Alzol Red (product of Futaba Chemical ResearchInstitute), Orient Oil Red 5B (trademark of Orient Chemical IndustriesCo., Ltd.), Casset Red 802 (trademark of Nippon Kayaku Co., Ltd.), OilRed SA Extra (trademark of Shirado Chemical Research Institute), etc.Anthraquinone pigments are exemplified by Casset Blue-814 (trademark ofNippon Kayaku Co., Ltd.), Oriental Oil Blue-K (trademark of Toyo Ink,Co., Ltd.), Sumiplast Blue-CA (trademark of Sumitomo Chemical IndustriesCo., Inc.), etc. A red azo pigment, xylyl-azoxylydene-2-napthole, is apreferred pigment.

[0061] It is preferred that pigment component (D) be soluble in theorganopolysiloxane of component (A). Component (D) should be used in anamount sufficient for coloring the silicone rubber composition .Typically, it can be used in an amount of 0.05 to 2,000 ppm relative tothe amount of component (A). If the pigment is used in an amount lessthan 0.05 ppm, the effect of the coloration of the silicone rubberadhesive film of the invention will be insufficient. If the amount ofpigment exceeds 2,000 ppm, the film-like adhesive becomes too hard andwill be unsuitable for the purposes of the present invention.

[0062] There are two methods by which component (D) can be added to thesilicone rubber adhesive film of the present invention. In the firstmethod, component (D) is introduced directly to the silicone rubbercomposition by kneading the pigment into the mixture. Alternatively, thepigment is impregnated into the silicone rubber adhesive film. Themethod of impregnation involves contacting the surface of the siliconerubber adhesive film with a pigment, component (D) for approximately onehour.

[0063] For bonding a metal substrate to a glass substrate, the surfaceof the metal substrate is often first treated with a primer. Thisimproves the adhesion of the silicone rubber adhesive film to the metalsubstrate. In these cases, component (D) is first added to the primercomposition, and then the silicone rubber adhesive film is contactedwith the surface of the primer-treated surface, wherein component (D)penetrates from the primer-treated surface to color the silicone rubberadhesive film.

[0064] One embodiment of the method of adhesion of the instant inventioninvolves;

[0065] 1) coating the surface of a metal substrate with a primercomposition comprising a organosilicon compound selected from the groupof silanes and organosiloxane oligimers having an alkoxy group to form aprimer layer;

[0066] 2) laminating said primer layer with the colored silicone rubberadhesive film described above;

[0067] 3) bringing the surface of said colored silicone rubber adhesivefilm into contact with a glass substrate;

[0068] 4) curing said colored silicone rubber adhesive film compositionat a temperature above 80° C. until the said colored silicone rubberadhesive film composition becomes colorless.

[0069] The first step comprises coating the surface of a metal substratewith a primer composition having its main components in the form of anorganosilane, which contains at least one alkoxy group or anorganosiloxane oligomer which contains at least one alkoxy group. Themetal substrate is exemplified by stainless steel, iron, aluminum, orzinc. The primer composition used may have as its main components anorganosilane, which contains alkoxy groups and / or an organosiloxaneoligomer which contains alkoxy groups. The primer composition may or maynot contain an azo pigment or an anthraquinone pigment. The primercomposition may consist of, for example, an organic solvent, an organictitanium compound and a polysiloxane, which contains an ethoxy groupsuch as tetraethoxysilane or a product of hydrolysis and condensation ofa tetraethoxysilane. There are no particular limitations regarding howthe primer composition is to be applied. In the case of the primercomposition containing an organic solvent, it is preferred that theorganic solvent be completely removed by air drying after the primercomposition has been applied.

[0070] In step 2, the colored silicone rubber adhesive film, asdescribed above, is contacted with the primer-treated surface obtainedin step 1. If desired, the silicone rubber adhesive film can be cut intoa shape matching the shape of the metal substrate, and then the cut-outsilicone rubber adhesive film is placed onto the primer-treated layer.In performing this step it is preferable to adhere the colored siliconerubber adhesive film to the primer-treated surface with the applicationof light pressure.

[0071] Then in step (3) a glass substrate is contacted with the surfaceof the silicone rubber adhesive film. It is preferred that contactbetween the glass substrate and the silicone rubber adhesive film becarried out under pressure sufficient for compressing and deforming thefilm-like adhesive so that sufficient contact occurs between thesilicone rubber adhesive film and the glass substrate. Normally, thispressure should be within a range of 0.1 to 20 kg/cm².

[0072] In step (4), the film-like adhesive is then cured by heating to atemperature exceeding 80° C. As a result, the color obtained due to theazo pigment or the anthraquinone pigment fades and heating is continueduntil complete decoloration. It is preferred that heating be within atemperature range of 100-170° C.

[0073] As a result, an integral structure consisting of a metalsubstrate and a glass substrate strongly bonded to each other is thusobtained.

[0074] In another embodiment of the method of the invention comprisesthe following steps:

[0075] 1) coating the surface of a metal substrate with a primercomposition comprising,

[0076] i) an organosilicon compound having an alkoxy group selected fromthe group of silanes and organosiloxane oligimers, and

[0077] ii) a pigment selected from the group of azo pigments andanthroquinone pigments

[0078] to form a colored primer layer on the surface of said metalsubstrate;

[0079] 2) laminating said colored primer layer with a silicone rubberadhesive film composition comprising,

[0080] (A) 100 parts by weight of an organopolysiloxane with an averageunit formula R_(a)SiO_((4-a)/2), where R is a substituted orunsubstituted hydrocarbon group with the provisio that at least two Rgroups are alkenyl groups, and a is a number between 1.9 and 2.1;

[0081] (B) 30 to 150 parts by weight of a wet method hydrophobizedreinforcing silica having a specific surface area exceeding 200 m²/g,consisting essentially of SiO_(4/2) units and organopolysiloxane unitsselected from the group consisting of R₃SiO_(1/2) units, R₂SiO_(2/2)units, RSiO_(3/2) units, and mixtures thereof, where R is the same asdefined above,

[0082] wherein the mole ratio of the organopolysiloxane units to theSiO_(4/2) units is within a range of 0.08 to 2.0;

[0083] (C) 0.1 to 10 parts by weight of an organohydridopolysiloxanecomprising at least one silicon-bonded hydrogen atom;

[0084] (E) a curing accelerator in an amount sufficient to cure thesilicone rubber adhesive film composition;

[0085] wherein said silicone rubber adhesive film composition has atensile strength of 1.5 kg/cm² to 5.0 kg/cm² at 25° C.;

[0086] 3) maintaining contact between the silicone rubber adhesive filmand the colored primer layer for at least one hour to form a coloredsilicone rubber adhesive film;

[0087] 4) bringing the surface of said colored silicone rubber adhesivefilm into contact with a glass substrate, and

[0088] 5) curing said colored silicone rubber adhesive film by heatingat a temperature above 80° C. until the film becomes colorless.

[0089] In carrying out the method of this embodiment of the invention,first in Step (1) a primer composition that contains an azo pigment oran anthraquinone pigment is applied onto the surface of a metalsubstrate. The metal substrate can be made of stainless steel, iron,aluminum, zinc, etc. The primer composition comprises an azo pigment oran anthraquinone pigment, as described above, added to a compositionwhich has as its main components an organosilane with alkoxy groups oran organopolysiloxane with alkoxy groups as described above. The primercomposition may comprise, for example, an organic solvent, an azo oranthraquinone pigment, an organic titanium compound, and a siloxaneoligomer with an ethoxy group, which is either a tetraethoxysilaneitself or a product of hydrolysis and condensation of thetetraethoxysilane. There are no special limitations regarding the mannerin which the primer composition has to be applied. When the primercomposition contains an organic solvent, the organic solvent isgenerally removed by air drying after the primer composition has beenapplied.

[0090] In step (2) of this embodied method, the silicone rubber adhesivefilm of the present invention is brought into contact with theprimer-treated surface obtained in Step (1). If desired, the siliconerubber adhesive film can be cut into a shape matching the shape of themetal substrate. The cut-out silicone rubber adhesive film is thenplaced onto the primer-treated layer. It is preferable to adhere thesilicone rubber adhesive film to the primer-treated surface with theapplication of light pressure.

[0091] In step (3), the unit is then left intact for at least one hourto allow the azo or anthraquinone pigment to penetrate the siliconerubber adhesive film. There are no particular limitations regarding thetime the unit should be left intact for penetration. The time willdepend on the solubility of the azo or anthraquinone pigment in thesilicone rubber adhesive film, or on the thickness of the siliconerubber adhesive film, etc. Generally, the time should exceed one hourand preferably exceed 24 hours.

[0092] Then in step (4), a glass substrate is brought into contact withthe surface of the silicone rubber adhesive film. The glass substrateand the silicone rubber adhesive film is generally contacted withsufficient pressure to compress and deform the silicone rubber adhesive.Normally, this pressure should be within a range of 0.1 to 20 kg/cm².

[0093] In step (5), the adhesive film is then cured by heating at atemperature exceeding 80° C. and the color obtained due to the azopigment or the anthraquinone pigment fades. Heating is continued untilthe silicone rubber adhesive film becomes colorless. A temperature rangeof 100-170° C. is preferred to assure the metal substrate and the glasssubstrate are strongly bonded to each other.

[0094] The silicone rubber adhesive film described above is convenientfor handling and possesses excellent workability. In particular, when itis used for applying a substrate for adhesion, the degree of curing ofthe silicone rubber adhesive film is controlled and creates an adhesiveconnection with greater uniformity in the adhesive strength. Thiscomposition can be used in fields, which require such improved adhesionproperties, for example, bonding glass parts to metal parts. Examplesare attaching knobs to glass doors or to glass windows in buildings, andfor attaching mirrors (so called inner mirrors) to automobilewindshield, etc.

[0095] The invention will be further described with reference topractical examples. In the following practical examples all parts aregiven in terms of parts by weight and all percentages are given as wt.%.

EXAMPLES

[0096] The following procedure was used for measuring the tensilestrength of an uncured silicone rubber composition. A silicone rubbercomposition was formed into a 2 mm thick sheet by passing it between tworollers. The obtained sheet-like product was stamped into a standarddumbbell-type sample #2 in accordance with JIS K 6301 (Vulcanized RubberPhysical Test Processes). After that, the tensile strength of thedumbbell sample was tested in accordance with the provisions of JIS K6301. Measurements were carried out at a temperature of 25° C.

Reference Example 1 Synthesis of Wet method hydrophobized reinforcingsilica

[0097] A glass reactor was loaded with 118 g of methanol, 32 g ofconcentrated aqueous ammonium hydroxide and 41 g ofdimethyl-dimethoxysilane, and these components were stirred by means ofelectromagnetic stirring until a uniform mixture appeared. While themixture was stirred vigorously, 96 g of a methyl-orthosilicate wasadded. After 10 seconds, the reaction product turned into a gel-likesubstance, stirring was stopped, and the obtained product was leftintact, in a closed cool room for one week, whereby a dispersion ofwet-method wet method hydrophobized reinforcing silica was obtained. Themethanol and gaseous ammonia were removed from the silica dispersion.The BET surface area of the wet method hydrophobized reinforcing silicawas measured and the results of the measurements showed that theobtained wet-method hydrophobized reinforcing silica had a specificsurface area equal to 620 m²/g.

Reference Example 2 Synthesis of Wet method hydrophobized reinforcingsilica

[0098] First, a hydrophobization agent was prepared by a methoddescribed in Official Japanese Patent Publication (Kokoku) No. 61-56255.A reaction was conducted for 2 hours at 105° C. with 277 g of octamethylcyclotetrasiloxane, 4.6 g of1,3,5,7-tetramethyl-1,3,5,7-tetravinylsiloxane, 517 g ofmethyltrimethoxysilane, and 0.43 g of potassium hydroxide as a catalyst.As a result, a hydrophobization agent consisting of a ring-openedrearranged organopolysiloxane was prepared. The potassium hydroxide wasneutralized by carbon gas. Analysis of the obtained polysiloxane showedthat the product was made of a linear organopolysiloxane with 0.7 mole %of methyl vinyl siloxy groups.

[0099] Then, the wet method hydrophobized reinforcing silica wassynthesized as follows with the use of the obtained hydrophobizationagent. A glass reactor was loaded with 118 g of methanol, 32 g ofconcentrated aqueous ammonium hydroxide and 39 g of the hydrophobizatonagent obtained above. These components were stirred by means ofelectromagnetic stirring until a uniform mixture appeared. While themixture was stirred vigorously, 96 g of a methyl-orthosilicate wasadded. After 10 seconds, the reaction product turned into a gel-likesubstance, stirring was stopped, and the obtained product was leftintact, in a closed cool room to age for one week whereby a dispersionof wet method hydrophobized reinforcing silica was obtained.

[0100] The methanol and gaseous ammonia were removed from the silicadispersion. The BET surface area of the wet-method hydrophobizedreinforcing silica was measured and the results of the measurementsshowed that the obtained wet-method hydrophobized reinforcing silica hada specific surface area equal to 540 m²/g.

Example 1

[0101] First, 300 parts of the wet method hydrophobized reinforcingsilica dispersion (with the silica comprising 25% of the weight)obtained in Reference Example 1 and 100 parts of a copolymer rubber(with a degree of polymerization equaling 3,000) obtained frommethylvinylsiloxane and dimethylsiloxane having molecular chainterminals capped with dimethylvinylsiloxy groups (where dimethylsiloxaneunits comprised 99.63 mole % and methylvinylsiloxane units comprised0.37 mole %) were loaded into a kneader-mixer and mixed. The solvent wasremoved by heating to 90° C. After the volatile components werecompletely removed, a silicone rubber base was obtained. Then, 100 partsof the obtained silicone rubber base were combined with the followingcomponents: 1.5 parts of a copolymer (where the content of thesilicon-bonded hydrogen atoms was 1.52 wt. %) of dimethylsiloxane andmethylhydridosiloxane having a viscosity of 7 mm²/s at 25° C. andmolecular terminals blocked with trimethylsiloxy groups having aviscosity of 7 mm²/s at 25° C.; a complex of a chloroplatinic acid andtetramethyldivinylsiloxane in an amount that makes the content of aplatinum metal catalyst equal to 10 ppm; 100 ppm of methyltris(methylisobutynoxy) silane; 0.5 parts of γ-methacryloxypropyl trimethoxysilane, 0.5 parts of γ-glycidoxypropyl-trimethoxysilane; 0.4 parts ofglycerin monoaryl ether. As a result, a transparent silicone rubbercomposition was prepared. The obtained silicone rubber composition wascombined with 0.03 parts of a red azo pigment(xylyl-azoxylydene-2-napthole), to produce a silicone rubber compositionof red color. Tensile strength of this silicone rubber composition in anuncured state was measured and showed a magnitude of 2.6 kg/cm². Theobtained silicone rubber composition was extruded into a film-likeproduct through an appropriate extruder nozzle, whereby a 1.0 mm-thickand 5 cm-wide silicone rubber adhesive film was produced. The obtainedsilicone rubber adhesive was cut with a cutter knife into 1.0 mm-thick,2.0 cm-wide, and 3 cm-long pieces of a red silicone rubber adhesivefilm.

[0102] Meanwhile, the surface of a stainless-steel substrate (SUS403,20×30 mm) was coated with a primer composition consisting of 5 parts ofa product of hydrolysis and condensation of tetraethoxysilane, 1 part ofN-butyltitanate, and 94 parts of N-heptane. The coating was then leftintact at room temperature for 24 hours and air dried, whereby astructure having a transparent primer layer formed on the surface of thestainless-steel substrate was obtained. The red silicone rubber adhesivefilm was placed onto the surface of the primer layer, whereby alaminated structure in which the film-like silicone-rubber adhesive wasadhered to the stainless-steel substrate via the primer layer, wasproduced. The surface of the silicone rubber adhesive film was thenpressed to a preliminarily prepared glass substrate under a pressure of13 kg/cm at 130° C., and the adhesive connection was cured by heatingthe adhesive until the red color completely disappeared and the adhesivewas thus cured. In this case, heating was continued for 25 min. Theobtained assembly comprised an integral unit consisting of astainless-steel substrate and a glass substrate strongly adhered to eachother via a transparent silicone rubber adhesive film. Measurementshowed that in this structure the strength of the adhesive connectionbetween the stainless-steel substrate and the glass substrate was 52kg/cm².

Example 2

[0103] First, 300 parts of the wet-method hydrophobized reinforcingsilica dispersion (with the silica comprising 25% of the weight)obtained in Reference Example 2 and 100 parts of a copolymer rubber(with a degree of polymerization equaling 3,000) obtained frommethylvinylsiloxane and dimethylsiloxane having molecular chainterminals capped with dimethylvinylsiloxy groups (where dimethylsiloxaneunits comprised 99.63 mole % and methylvinylsiloxane units comprised0.37 mole %) were loaded into a kneader-mixer and mixed. The solvent wasremoved by heating to 90° C. After the volatile components werecompletely removed, a silicone rubber base was obtained. Then, 100 partsof the obtained silicone rubber base were combined with the followingcomponents: 1.5 parts of a copolymer (where the contents of thesilicon-bonded hydrogen atoms was 1.52 wt. %) of dimethylsiloxane andmethylhydridosiloxane having molecular terminals blocked withtrimethylsiloxy groups with a viscosity of 7 mm²/s at 25° C.; a complexof a chloroplatinic acid and tetramethyldivinylsiloxane in an amountthat makes the content of a platinum metal catalyst equal to 10 ppm; 100ppm of methyl-tris (methylisobutynoxy) silane; 0.5 parts ofγ-methacryloxypropyl trimethoxysilane, 0.5 parts ofγ-glycidoxypropyl-trimethoxysilane; and 0.4 parts of glycerin monoarylether. As a result, a transparent silicone rubber composition wasprepared. Tensile strength of this silicone rubber composition in anuncured state was measured and showed a magnitude within the range of3.0 to 3.5 kg/cm². The obtained silicone rubber composition was extrudedinto a film-like product through an appropriate extruder nozzle, wherebya 0.75 mm-thick and 5 cm-wide silicone rubber adhesive film wasproduced. The obtained silicone rubber adhesive was cut with a cutterknife into 0.75 mm-thick, 2.0 cm-wide, and 3 cm-long pieces of atransparent silicone rubber adhesive film.

[0104] Meanwhile, the surface of a stainless-steel substrate, as shownin FIG. 1 (1), (SUS403, 20×30 mm) was coated with a primer compositioncolored red by means of an azo-type pigment, as shown in FIG. 1 (2). Thered primer composition was prepared from 5 parts of the product ofhydrolysis and condensation of tetraethoxysilane, 1 part ofN-butyltitanate, 94 parts of N-heptane, and 1 part of red pigment(xylylazoxylydene-2-naphthol). According to Step (1), the coating wasleft intact at room temperature for 24 hours and air dried, whereby astructure having a red primer layer formed on the surface of thestainless-steel substrate was obtained (see FIG. 1).

[0105] In Step (2), the transparent silicone rubber adhesive film asshown in FIG. 2 (3) was placed onto the surface of the primer layer,whereby a laminated structure in which the film-like silicone-rubberadhesive was attached to the stainless-steel substrate via the primerlayer, was produced (see FIG. 2). The obtained structure was left intactfor 7 days at room temperature, whereby the transparent film-likesilicone turned red (see FIG. 3 (4)).

[0106] Then in Step (3), the surface of the silicone rubber adhesivefilm was pressed to a preliminarily prepared glass substrate, as shownin FIG. 4 (6) under a pressure of 13 kg/cm² at 130° C., and the adhesiveconnection was cured by heating the adhesive until the red hadcompletely disappeared. In this case, heating was continued for 30 min.The obtained assembly comprised an integral unit consisting of astainless-steel substrate and a glass substrate strongly adhered to eachother via a transparent silicone rubber adhesive film (see FIG. 4 (5)).Measurement showed that in this structure the strength of the adhesiveconnection between the stainless-steel substrate and the glass substratewas 62 kg/cm².

[0107] It has been shown that the colored film-like silicone-rubberadhesive of the invention is extremely convenient for handling andpossesses good workability. In particular, when it is used for adhesionof substrates, it becomes possible to verify the degree of curing of thesilicone rubber adhesive film to determine the moment when the curing iscompleted and to produce a bonded structure with reduced scattering inthe adhesive strength.

That which is claimed:
 1. A method of adhering a metal substrate to aglass substrate comprising: a) coating the surface of a metal substratewith a primer composition comprising a organosilicon compound selectedfrom the group of silanes and organosiloxane oligimers having at leastone alkoxy group to form a primer layer; b) laminating said primer layerwith a colored silicone-rubber adhesive film composition comprising: (A)100 parts by weight of an organopolysiloxane with an average unitformula R_(a)SiO_((4-a)/2), where R is a substituted or unsubstitutedhydrocarbon group with the provisio that at least two R groups arealkenyl groups, and a is a number between 1.9 and 2.1; (B) 30 to 150parts by weight of a wet method hydrophobized reinforcing silica havinga specific surface area exceeding 200 m²/g, consisting essentially ofSiO_(4/2) units and organopolysiloxane units selected from the groupconsisting of R₃SiO_(1/2) units, R₂SiO_(2/2) units, RSiO_(3/2) units,and mixtures thereof, where R is the same as defined above, and whereinthe mole ratio of the organopolysiloxane units to the SiO_(4/2) units iswithin a range of 0.08 to 2.0; (C) 0.1 to 10 parts by weight of anorganohydridopolysiloxane comprising at least one silicon-bondedhydrogen atom; (D) a pigment selected from the group of azo pigments andanthroquinone pigments present in an amount sufficient for coloring thesilicone rubber adhesive film composition; and (E) a curing acceleratorin an amount sufficient to cure the silicone rubber adhesive filmcomposition; wherein said colored silicone rubber adhesive filmcomposition has a tensile strength of 1.5 kg/cm² to 5.0 kg/cm² at 25°C.; c) bringing the surface of said colored silicone rubber adhesivefilm into contact with a glass substrate; d) curing said coloredsilicone rubber adhesive film composition at a temperature above 80° C.until the said colored silicone rubber adhesive film composition becomescolorless.
 2. The method of claim 1 wherein the contact between saidsilicone rubber adhesive film and glass substrate is applied with apressure between 0.1 to 20 kg/cm².
 3. A method of adhering a metalsubstrate to a glass substrate comprising: a) coating the surface of ametal substrate with a primer composition comprising, i) anorganosilicon compound having at least one alkoxy group selected fromthe group of silanes and organosiloxane oligimers, and ii) a pigmentselected from the group of azo pigments and anthroquinone pigments, toform a colored primer layer on the surface of said metal substrate; b)laminating said colored primer layer with a silicone rubber adhesivefilm composition comprising, (A) 100 parts by weight of anorganopolysiloxane with an average unit formula R_(a)SiO_((4-a)/2),where R is a substituted or unsubstituted hydrocarbon group with theprovisio that at least two R groups are alkenyl groups, and a is anumber between 1.9 and 2.1; (B) 30 to 150 parts by weight of a wetmethod hydrophobized reinforcing silica having a specific surface areaexceeding 200 m²/g, consisting essentially of SiO_(4/2) units andorganopolysiloxane units selected from the group consisting ofR₃SiO_(1/2) units, R₂SiO_(2/2) units, RSiO_(3/2) units, and mixturesthereof, where R is the same as defined above, wherein the mole ratio ofthe organopolysiloxane units to the SiO_(4/2) units is within a range of0.08 to 2.0; (C) 0.1 to 10 parts by weight of anorganohydridopolysiloxane comprising at least one silicon-bondedhydrogen atom; (E) a curing accelerator in an amount sufficient to curethe silicone rubber adhesive film composition; wherein said siliconerubber adhesive film composition has a tensile strength of 1.5 kg/cm² to5.0 kg/cm² at 25° C.; c) maintaining contact between the silicone rubberadhesive film and the colored primer layer for at least one hour to forma colored silicone rubber adhesive layer; d) bringing the surface ofsaid colored silicone rubber adhesive film into contact with a glasssubstrate, and e) curing said colored silicone rubber adhesive film byheating at a temperature above 80° C. until the film becomes colorless.4. The method of claim 3 wherein the organopolysiloxane has a degree ofpolymerization greater than 3000 and a viscosity greater than 1×10⁶mm²/s.
 5. The method of claim 3 wherein the mole ratio of theorganopolysiloxane units to the SiO_(4/2) units is within a range of0.08 to 1.5.
 6. The method of claim 3 wherein the pigment is an azopigment selected from the group consisting of monoazo pigments, diazopigments, polyazo pigments, pyrazolone pigments, stilbene azo pigments,and thiazole.
 7. The method of claim 3 wherein the pigment isxylyl-azoxylydene-2-napthole.
 8. The method of claim 3 wherein thecuring accelerator is selected from the group consisting of, organicperoxides, platinum catalysts, and combinations thereof.
 9. The methodof claim 3 wherein the adhesion accelerator comprises anorganoalkoxysilane having organic functional groups selected from thegroup consisting of mercapto groups, amino groups, vinyl groups, allylgroups, hexenyl groups, methacryloxy groups, acryloxy groups, glycidoxygroups, and the partial hydrolyzation and condensation products of thesaid organoalkoxysilanes.
 10. The method according to claim 1 whereinsaid metal substrate is selected from the group consisting of stainlesssteel, iron, aluminum, and zinc.
 11. The method according to claim 3wherein said metal substrate is selected from the group consisting ofstainless steel, iron, aluminum, and zinc.